I need to review an MP4 video for a work project. I use OS 10.8.3. The video downloaded and Quicktime opened automatically when I tried to play it. But I get a message saying Quicktime can't play it. What else do I need to download so that Quicktime can play an MP4 video and where do I find it? Or is there something other than Quicktime I should use to open it? Thank you.